<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <link rel="stylesheet" href="../BootstrapPractise/bootstrap/css/bootstrap.css">
    <style type="text/css">
        .div1{
            border:1px red solid;
        }
    </style>
    <script type="text/javascript">
        function change(){
            var a=document.getElementById("btna");
            a.className="div1";//给id=btna的标签赋值class

        }
        function hide(){
            var a=document.getElementById("btna");
            a.style.display="none";//隐藏。
        }
    </script>
</head>
<body>
<div id="btna">123</div>

<button  class="btn btn-info" onclick="change()">addBorder </button>
<button  class="btn btn-info" onclick="hide()">hide </button>
</body>
</html>